Rhiannon Davies (née Jones) was the sister of Torchwood member Ianto Jones.
Rhiannon and her husband lived on the Cromwell council estate with their two children, David and Mica. Both children were briefly taken over by the 456. Rhiannon had not seen much of Ianto before the 456 event, but they had apparently kept in touch.
She took a mature attitude with him about leaving the family just after their father died, thinking he did not care about them anymore. She also seemed accepting of his relationship with Jack and even comforted him when he told her he was not entirely sure what sort of relationship it was.
She was not aware that her brother worked for Torchwood. She thought he was a civil servant. (TV: Children of Earth: Day One)
Later, during the 456 incident, Rhiannon needed to exit her house without the members of the government, who were spying on them, seeing. This gave Johnny the idea of accusing the officials of being "paedos" and getting the local neighbourhood children to shake the car about, this gave Rhiannon enough time to leave in her car.
She eventually left and met with her brother Ianto in a park. There they discussed current affairs, additionally she let Ianto borrow both her laptop and her car. (TV: Children of Earth: Day Two)
She later ran a creche, opened by Johnny, for "ten quid a kid", this enabled parents to go to work during the curfew which was held in place for the children's safety. There she witnessed the kids once again being used as hosts by the 456. (TV: Children of Earth: Day Three)
Later she received a call from Ianto telling her to not let the kids go to school and that the government were lying to the people of Earth. After this Rhiannon told her son David Davies to warn the locals about what Ianto had told them, she told him to say her brother worked for the government. Johnny and Rhiannon kept the creche going because of this, however this time for free. (TV: Children of Earth: Day Four, Day Five)
She later was paid a visit by Gwen Cooper, Rhys Williams and Andy Davidson. They informed Rhiannon of Ianto's death and pleaded to them that they needed to flee.
They eventually ran with the children that were in their care taking them to a safe place. Unfortunately for her, they were found but they kept on running. They were caught up with by the British Army but later released when the 456 incident was officially over. (TV: Children of Earth: Day Five)